The idea of the TL Meltagun is the better chance to actually get a hit. With the MM, you have one dice chance to get it right with each oblit. If you facing 13-14 armour in front of you, then I would say use the MM. Anything under that, stick to the TL Meltagun.
And people who just want to bring their transports right in front of your oblits to not allow u a firing lane, I will gladly just stick a rhino in front of oblits for a turn to allow the rest of my army to work while your oblits can shoot at mainly one thing. Or just to almost let you kill the transport so whatever inside can fire and/or assault at you next turn, if its still alive.
